Nitrous oxide (N2O), commonly known as laughing gas, can be a product of the combustion of carbon-containing materials, such as hydrocarbons, and nitrogen bearing compounds, such as ammonia (NH3). Other combustion products include the nitrogen oxides of NO and NO2, both together may be referred to as NOx. Nitrous oxide is considered to be a greater contributor to the greenhouse effect and global warming than certain other greenhouse gases such as carbon dioxide (CO2), and it would be desirable to have a process that is able to economically remove contaminating concentrations of nitrous oxide contained in combustion gases that are released into the atmosphere.
The prior art generally has been focused more on the reduction of nitrogen oxides that are contained in combustion gases rather than on the removal of nitrous oxide. One process used for the removal of NOx from gas streams is the selective catalytic reduction (SCR) process. One version of this process is disclosed in U.S. Pat. No. 7,294,321. In this selective catalytic reduction process, a combustion gas that contains a concentration of NOx and ammonia (NH3), which is typically added to the combustion gas as a reactant, is contacted with a catalyst that promotes the reduction reaction in which the NOx reacts with ammonia and oxygen to yield nitrogen and water.
Disclosed in U.S. Pat. No. 7,459,135 is a catalyst used for the catalytic reduction of NOx. This catalyst comprises a palladium-containing zeolite, wherein the zeolite also comprises scandium or yttrium or a lanthanide or combinations thereof. The teachings of U.S. Pat. No. 7,459,135 are not concerned, however, with the catalytic decomposition of nitrous oxide. One process that does, on the other hand, involve the catalytic decomposition of nitrous oxide contained in a gas is the process disclosed in U.S. Pat. No. 6,143,262. In this process, a gas that contains nitrous oxide is contacted with a catalyst that comprises mainly tin oxide, but it further may include cobalt as a co-catalyst.
Another process for the catalytic decomposition of nitrous oxide is disclosed in US 2008/044334. This publication teaches a catalyst that is used for the catalytic decomposition of nitrous oxide (N2O) to yield nitrogen (N2) and oxygen (O2). The broadly disclosed catalyst of US 2008/044334 comprises a zeolite that has been loaded with a first noble metal and a second transition metal. The first metal is selected from the group consisting of ruthenium (Ru), rhodium (Rh), osmium (Os), and iridium (Ir), and the second metal is selected from the group consisting of iron (Fe), cobalt (Co), and nickel (Ni).
Due to nitrous oxide being a greenhouse gas having a global warming potential that is significantly greater than certain other greenhouse gases, it is desirable to have a process for the removal of nitrous oxide from gas streams that have high concentrations of nitrous oxide and are released into the atmosphere. It is further desirable for such a process to achieve the removal of nitrous oxide in a cost-effective, thermally efficient manner.